Method for applying hard facing to an object

ABSTRACT

The nose of a chain saw blade is radiused along its edges. The radiused nose is then grit blasted to roughen its surface and to remove any oxides. A first layer of particulate hard facing material is applied to the radiused nose and fused to obtain a metallurgical bond between the nose and the first layer. A second layer of hard facing is then welded to the prepared first layer with an inert gas shielded arc process without marked penetration into the nose&#39;&#39;s parent material. The hard facing is then finished by grinding.

United States Patent 91 Espana et al.

111 3,760,141 1 Sept. 18, 1973 1 METiiofiFoR APPLYING HARD FACING TO ANOBJECT [75] lnventors: Salvador Espana, San Pedro, Calif.;

Brunson Bert Font, Lake Havasu City, Ariz.

[73] Assignee: McCulloch Corporation, Los

Angeles, Calif.

[22] Filed: Oct. 4, 1971 [21] Appl. No.: 186,437

Related US. Application Data [62] Division of Ser. No. 852,587, Aug. 25,1969,

abandoned.

[52] US. Cl. 219/77 [51] Int. Cl 823k 9/04 [58] Field of Search 219/76,77

[56] References Cited UNITED STATES PATENTS 2,962,812 12/1960 Gommel .L143/32 H X 3,133,184 5/1964 Rienhoff et al.. 219/76 3,566,069

2/1971 Henderson 219/70 R22,398 11/1943 Meduna 219/76 X 1,602,995 10/ l926 Wissler 2,71 1,467 6/1955 Malcolm 1,790,213 l/l931 Gwaltney3,071,490 1/1963 Pevar 219/76 X OTHER PUBLICATIONS Welding Handbook 1942TS227A5h, pp. 605-615 Primary Examiner-R. F. Staubly Attorney-Christie,Parker & Hale [57] ABSTRACT The nose of a chain saw blade is radiusedalong its edges. The 'radiused nose is then grit blasted to roughen itssurface and to remove any oxides. A first layer of particulate hardfacing material is applied to the-radiused nose and fused to obtain ametallurgical bond between the nose and the first layer. A second layerof hard facing is then welded to the prepared first layer with an inertgas shielded arc process without marked penetration into the nosesparent material. The hard facing is then finished by grinding.

12 Claims, 10 Drawing Figures 1 METHOD FOR APPLYING HARD FACING TO ANOBJECT This is a division, of application Ser. No. 852,587 filed Aug.25, 1969, now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to theapplication of hard facing onto objects such as a chain saw blade, and,more in particular, to a method of effecting a hard faced object whichapplies hard'facing materials in at least two layers to preventoverpenetration and the consequent presence of excessive iron from theparent material in the hard facing.

The nose of a steel chain saw blade has a generally circular'tip and tworelatively straight, slightly diverging edges extending from the tip.The radius of the circular tip is relatively small.

I-Iard facing is applied to the nose of chain saw blades to promotebetter wear characteristics inasmuch as it is this area which is subjectto considerable heat and wear by the chain as it tracks on the blade,especially during the making of a cut.

For the type of environment the hard facedblade is subjected to, it isdesirable, not to have the hard facing material too hard for it must betough enough to withstand impact. Yet the hard facing must have goodwear characteristics. Cobalt based hard facing has been found to satisfythe conflicting requirements of wear and toughness.

Heretofore, the application of cobalt based hard facaffecting themetallurgical bond between the initial layer and the parent material.

In more specific form, the present invention envisions the applicationof a cobalt based hard facing to a steel object in an area which isrelativelythin, as is the nose of a chain saw blade. The edges of theobject bounding the area to be hard faced are radiused, by an arc torch,milling or other suitable method, to prevent parent iron from enteringinto the initial and subsequent layers of hard facing. The surface ofthe area to be hard faced is then cleaned as by a grit blast to roughenit and to remove any oxides. Preferably, a sharp metallic grit is usedto avoid the inclusion of silicon in the hard facing and its consequentweakening. The initial layer of cobalt based hard facing is applied tothe object, as thus radiused, in particulate form by a flame sprayprocess to obtain a mechanical bond. The applied particles are fused insuch a manner that the melting temperature of the parent material is notexceeded and a metallurgical bond between the initial layer and theparent material is formed. The bulk of the hard facing is then'appliedto the initial layer, preferably by a shielded arc, such as a heliarc,to obtain low porosity in thefinished hard facing. The hard facedobject' is then finished as by grinding.

ing to the noseof a chain saw-blade byan inert gas SUMMARY OF THEINVENTION The present invention provides a process for hard facing anobject, such as a chain saw blade, preferably by an inert gas shieldedarc process, which prevents excessive dilution of the blades parentmaterial into the hard facing.

The process envisions the application of an initial hard facing layerapplied in such a manner that dilution of parent material into itoccurs, if at all, to a limited and acceptable extent. The inventionalso provides an object which has a hard facing which is notdetrimentally affected by the presence of an excessive amount of parentmaterial.

In one form, the present invention contemplatesa processwherein aninitial coating of hard facing is applied to the area of an object to behard faced in such a manner that a metallurgical bond between the layerof hard facing and the parent metal of the object is formed. Themetallurgical bond between the initial layer of hard facing and theobject is sometimes referred to as a sweat" bond and is akin to a brazedbond. The bond is distinguished from a weld bond in that theparentmaterial is not melted. Because the parent material is not melted,dilution of parent material in the hard facing is minimal. A second ormore layers of hard facing may then be applied to the initial layer tocomplete the hard faced object without substantially During theapplication of the bulk of the hard facing to the first layer, some ironfrom the parent steel may enter the first layer. Because of this, theparticular hard facing material chosen for the initial layer is chosenfor its strength compatibility with a small amount of iron. The bulk ofthe hard facing which will not contain any material amount of iron ischosen for its wear, toughness, and compatibility with the initiallayer. Because the composition of the initial and subsequent layers willchange with their application, the finished chain saw blade may beviewed as having an initial zone of hard facing and a subsequent zone ofhard facing.

The process and object produced by the process of the present inventionassures a hard facing which does not have a material amount of parentmaterial. The application of the initial layer of hard facing to theobject to obtain a metallurgical bond prevents the parent material fromreaching its melting temperature. This prevents dilution of parentmaterial into the hard facing. The subsequent application of the secondor more layers of hard facing to the initial layer may dilute theinitial layer with a small amount of parent iron; but this dilution doesnot materially affect the resulting strength of the hard facing becausethe metallurgical bond between the initial layer and the parent materialis not affected.

In short, the initial layer of hard facing provides a barrier betweenthe parent material and the final layers of hard facing. The barrierprevents an excessive amount of parent material from mixing with thehard facing to weaken it.

These and other features, aspects and advantages of the presentinvention will become more apparent from the following description,appended claims and drawmgs.

. BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a plan view. of a'hardfaced chain saw blade; FIG. 2 is a block diagram depicting the hard faceapplication process of the present invention;

FIG. 3 is an end view of a chain saw blade before the application ofhard facing to it and before it has been prepared for receiving hardfacing;

FIG. 4 is an end view of a chain saw blade after the edges of the areato be hard faced have been radiused;

FIG. 5 is an end view of a chain saw blade illustrating the applicationof an initial layer of hard facing material;

FIGS. 6 through 9 schematically depict both the application of theinitial hard facing layer and the application of the final hard facinglayers; and

FIG. 10 illustrates an apparatus suitable for the application of theinitial layer of hard facing material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a steelchain saw blade 10 which has a nose 12 on which successive layers ofcobalt based hard facing material 14 have been applied. The chain sawblade has a medial slot or groove indicated by reference numeral 16 forthe tracking of the chain portion of the chain saw. The chaincontinuously circumscribes the blade and has means for effecting a cutin a log or the like. I

The chain saw blade is of a high carbon steel having about 0.8 percentcarbon and about 1 percent manganese. The particular steel is known as amodified 1074 steel.

The chain saw is used in cutting by bringing nose 12 to bear on a log orthe like. This produces a high friction force on the nose. Augmentingthis friction force is a relatively sharp radius of the tip of .thenose. The wear area of the nose is also relatively small because theblade is relatively thin. Because of these factors, cobalt hard facing14 is used.

Unfortunately, however, prior art methods of hard facing a chain sawblade by a shielded arc process have not been satisfactory because theresulting hard facing exhibits poor wear characteristics.

It has been found that the application of cobalt based hard facing tothe chain saw blade, without producing a condition where iron from theparent material mixes with it to any significant extent, substantiallyenhances the wear resistance of the ultimate hard facing. Morespecifically, it has been found that with the presence of more thanabout 5 percent iron in the cobalt based hard facing material, thematerials wear properties are drastically compromised.

The application of an initial layer of hard facing material to the noseof a chain saw blade with a metallurgical or sweat bond constitutes ahard facing layer which acts as a barrier against iron from the bladeentering the hard facing material to any significant extent.

With reference to FIGS. 3, 4 and 5, a more detailed I description of theapplication of the initial layer of hard facing material to nose 12 ofchain saw blade 10 will be presented.

In FIG. 3, chain saw blade 10 initially has its nose with sharp edges 18between a surface 20 to be hard faced and sides 22 and 24 of the blade.These sharp edges result from the method of fabrication of the chain sawblade.

The initial step in the process is to round these sharp edges to obtaina radiused surface 26, as is illustrated in FIG. 4. This is preferablydone by removing material from the nose by an arc because it is fast,but milling or other suitable methods are adequate. The arc is appliedon the edges.

The elimination of the sharp edges overcomes a condition where iron fromthe nose can enter the hard facing because of the melting of the edgesduring the application of subsequent layers by an arc. Radiusing theedges also results in a uniform thickness of the initial layer of hardfacing material. A uniform thickness avoids thin areas where iron canenter the hard facing material during the application of the subsequentlayer to the initial layer, that is, a uniform thickness prevents theloss of the barrier property of the initial layer.

The surface of the parent material is then prepared for receiving theinitial layer of hard facing. This is done by cleaning the surface,preferably with a sharp metallic grit blast. This roughens the surfaceand cleans away any oxides which may have formed.

In FIG. 5, an initial layer 28 of hard facing has been applied.Application of this initial layer is preferably done by flame spraying apowder composition of a cobalt based hard facing material onto the zoneof the nose to be hard faced. During the flame spraying, the powderbonds to surface 28 with a mechanical bond.

A flame spraying may be done by the apparatus illustrated in FIG. 10. Inthe FIG. 10 apparatus, a jig 30 mounts several prepared blades 10. Thejig is carried on a shaft 32 of a DC motor 34. This motor is mounted ona table 36 which is capable of reciprocating movement parallel to theaxis of the blades by virtue of a screw drive 38 driven by DC motor 40.Motor 34 functions to rotate the blades back and forth through an arc ofa circle corresponding to the arc of the end of the noses of the blades.A flame sprayer 42 is mounted on a bracket 44. This bracket is mountedon a shaft 46 for reciprocating movement along a line normal to the axisof the blades being flame sprayed. A crank drive 48 from a DC motor 50reciprocates the flame sprayer back and forth across the noses of theblades to apply the initial layer of hard facing. During the applicationof the initial layer, the blades are rotated with respect to the flamesprayer in jig 30, to present their rounded nose. The length of thesides of the nose is presented to the flame sprayer by movement of table36, and the entire bundle of blades in jig 30 is sprayed because ofmovement of flame sprayer 42 across them.

Flame'sprayer 42 may be of any of a number of well known sprayers suchas a Model D-3 Sprayweld gun manufactured by Wall-Colmonoy Corp.,Detroit, Mich. The flame sprayer aspirates powder or particulate hardfacing material into a gas stream. The aspirated powder is heated by theburning of an oxidizer, such as oxygen, and a fuel, such as hydrogen oracetylene. The heated powder is transported in a gas stream to the noseof the blade where the mechanical bond between it and the nose occurs.

The spray applied initial layer is then fused with a gas torch or byinduction to obtain a metallurgical bond between the initial layer andthe nose of the chain saw blade.

The application of the final layer of hard facing is illustrated inFIGS. 6 through 9. In these Figures a blade is mounted in a machine formotion quite similar to the motion described with reference to FIG. 10.Thus, a traverse is made to the left in FIG. 6 of the blade for thepurpose of applying hard facing on initial layer 28 with an arc welder51. The blade is then rotated for the purpose of applying hard facing onthe initial area around a the 'rounded tip of the blade. This latterhard facing step is shown in FIG. 7. The blade is then once againtraversed to the left for the purpose of applying a hard facing to thebalance of the initial layer. FIG. 9 illustrates the blade as it wouldappear just prior to the completion of the application of hard facingmaterial to the nose. The developing hard facing on initial layer 28 isindicated by reference numeral 52.

. It rhasbeen found that an initial hard facing of a pow- .deredmaterial marketed as Wallex 50 manufactured by Wall-Colmonoy Corp., ofDetroit, Michigan, provides a very satisfactory initial layer. Theanalysis of this materialis shown in the table below:

TABLE I Constituent Percentage of Total Composition C .75 Cr 25.00 Ni11.00 B 3.00 Si 2.75 Fe 1.00 (maximum) W l .00 Co Balance The nickel,boron and silicon in the composition of Table I increases thefluidity ofthe composition during its application. Thus the amount of heat requiredto .apply and fuse the material can be relatively low to .avoid meltingparent material and .hard faced material.

getting it into the The alloy exhibits good toughness to withstand shockand a relatively high wear hardness to resist wear.

The finallayer or layers of hard facing material is preferably amodification of an alloy having the ASTM specification A-399-56T(RCoCr-A). This specification is to an alloy in rod form withconstituents shown in the following table:

It should be noted that the preferred alloy composition has lessthan lvpercent iron. This is because some iron reaches the hard facing materialduring the application of the hard facing from the chain saw bladeproper. As such, the amount of iron in the alloy before application isheld to a low percentage to admit to an increased amount of iron in thealloy as applied.

completed hard faced chain saw blade may be viewed as having an initialzone of hard facing on which a subsequent zone of hard facing has beenapplied.

After the application of the final hard facing, the hard facing isground to conform its sides to the sides of the saw blade and itsperiphery to the desired periphery of the nose. Slot 16 is then groundinto the blade and the hard facing material.

What is claimed is:

l. A process for hard facing an iron based object on a narrow areathereof bounded by closely spaced sides of the object comprising thesteps of:

a. applying an initial layer of cobalt based hard facing material to thearea in such a manner that a sweat bond is formed between the initiallayer and the object;

b. welding a subsequent layer of cobalt based hard facing to the initiallayer to form the hard faced object while maintaining the sweat bond;and

c. maintaining the iron content in both layers of hard facing belowabout five percent by maintaining the sweat bond throughout the processand limiting the amount of iron in both layers of hard facing.

2. The process claimed in claim 1 including the step of rounding theedges of the object between the narrow area and the sides before theapplication of the initial layer.

3. The process claimed in claim 2 including the step of cleaning andtoughening the surface of the parent material before the application ofthe initial layer of hard facing, and the subsequent layer is applied tothe I initial layer by arc welding the two together.

As was previously mentioned, the final hard facing is 4 v preferablyapplied by inert gas arc welding. With an arc application, the initiallayer and the final layers are welded together to form an essentiallyhomogeneous =hard facing except for composition gradients. Themetallurgical nature of the bond between the initial layer and theparent material of the'chain saw blade is not materially altered by theapplication of the subsequent layer. As such, the iron content in thehard facing does not exceed 5 per cent.

Because of the composition gradient through the initial layer and thesubsequent layer of hard facing, the

4. The process claimed in claim 3 wherein the initial layer of hardfacing is applied by flame spraying particulate hard facing material,and including the step of fusing the initial layer before theapplication of the subsequent layer of hard facing to obtain the sweatbond.

5. A process for hard facing a relatively thin steel object such as achain saw blade on a zone thereof bounded by closely spaced sidescomprising the steps of:

rounding the edges between the sides and the zone;

roughening the parent material;

flame spraying a particulate cobalt based hard facing material onto thezone to form an initial layer; fusing the initial layer to obtain asweat bond between the initial layer and the zone; welding a subsequentlayer of cobalt based hard facing to the initial layer; and

maintaining the iron content in both layers of hard facing below aboutfive percent by maintaining the sweat bond between the initial layer andthe parent material throughout the process and limiting the amount ofiron in both layers of hard facing.

6. The process claimed in claim 5 wherein the subsequent layer of hardfacing is welded to the initial layer by shielded arc welding.

7. The process claimed in claim 6 wherein the edges are rounded by anarc.

8. The process claimed in claim 7 wherein the parent material is cleanedand roughened by a metallic grit blast.

9. The process claimed in claim 8 wherein the initial layer of hardfacing prior to application comprises:

a. about 0.75 percent carbon;

b. about 25 percent chromium;

c. about 11 percent nickel;

d. about 3 percent boron;

e. about 2.75 percent silicon;

f. a maximum of 1 percent iron; g. about percent tungsten; and h. abalance of cobalt;

and the subsequent layer of hard facing prior to application comprises:

a. from about 0.9 percent to 1.4 percent carbon; b. a maximum of 0.1percent manganese; c. from about 0.4 to about 2.0 percent silicon; d.from about 26 to 32 percent chromium; e. up to 3 percent nickel; f. upto 1 percent molybdenum; g. from about 3 to about 6 percent tungsten; h.up to 3 percent iron; and i. a balance of cobalt.

10. The process claimed in claim 9 wherein the subsequent zone of hardfacing prior to application comprises:

a. about 1.3 percent carbon; b. about 1.2 percent silicon; c. about 28.5percent chromium; d. about 0.75 percent nickel; e. less than 0.05percent molybdenum; f. about 4.45 percent tungsten; and g. less than 1percent iron.

1 1. The process claimed in claim 1 wherein the initial layer of hardfacing prior to application comprises:

a. about 0.75 percent carbon;

b. about 25 percent chromium; 0. about 11 percent nickel;

d. about 3 percent boron;

e. about 2.75 percent silicon;

f. a maximum of 1 percent iron; g. about 10 percent tungsten; and h. abalance of cobalt;

and the subsequent layer of hard facing prior to application comprises:

sequent zone of hard facing prior to application comprises:

a. about 1.3 percent carbon;

b. about 1.2 percent silicon;

c. about 28.5 percent chromium;

d. about 0.75 percent nickel;

e. less than 0.05 percent molybdenum; f. about 4.45 percent tungsten;and

g. less than 1 percent iron.

2. The process claimed in claim 1 including the step of rounding theedges of the object between the narrow area and the sides before theapplication of the initial layer.
 3. The process claimed in claim 2including the step of cleaning and roughening the surface of the parentmaterial before the application of the initial layer of hard facing, andthe subsequent layer is applied to the initial layer by arc welding thetwo together.
 4. The process claimed in claim 3 wherein the initiallayer of hard facing is applied by flame spraying particulate hardfacing material, and including the step of fusing the initial layerbefore the application of the subsequent layer of hard facing to obtainthe sweat bond.
 5. A process for hard facing a relatively thin steelobject such as a chain saw blade on a zone thereof bounded by closelyspaced sides comprising the steps of: rounding the edges between thesides and the zone; roughening the parent material; flame spraying aparticulate cobalt based hard facing material onto the zone to form aninitial layer; fusIng the initial layer to obtain a sweat bond betweenthe initial layer and the zone; welding a subsequent layer of cobaltbased hard facing to the initial layer; and maintaining the iron contentin both layers of hard facing below about five percent by maintainingthe sweat bond between the initial layer and the parent materialthroughout the process and limiting the amount of iron in both layers ofhard facing.
 6. The process claimed in claim 5 wherein the subsequentlayer of hard facing is welded to the initial layer by shielded arcwelding.
 7. The process claimed in claim 6 wherein the edges are roundedby an arc.
 8. The process claimed in claim 7 wherein the parent materialis cleaned and roughened by a metallic grit blast.
 9. The processclaimed in claim 8 wherein the initial layer of hard facing prior toapplication comprises: a. about 0.75 percent carbon; b. about 25 percentchromium; c. about 11 percent nickel; d. about 3 percent boron; e. about2.75 percent silicon; f. a maximum of 1 percent iron; g. about 10percent tungsten; and h. a balance of cobalt; and the subsequent layerof hard facing prior to application comprises: a. from about 0.9 percentto 1.4 percent carbon; b. a maximum of 0.1 percent manganese; c. fromabout 0.4 to about 2.0 percent silicon; d. from about 26 to 32 percentchromium; e. up to 3 percent nickel; f. up to 1 percent molybdenum; g.from about 3 to about 6 percent tungsten; h. up to 3 percent iron; andi. a balance of cobalt.
 10. The process claimed in claim 9 wherein thesubsequent zone of hard facing prior to application comprises: a. about1.3 percent carbon; b. about 1.2 percent silicon; c. about 28.5 percentchromium; d. about 0.75 percent nickel; e. less than 0.05 percentmolybdenum; f. about 4.45 percent tungsten; and g. less than 1 percentiron.
 11. The process claimed in claim 1 wherein the initial layer ofhard facing prior to application comprises: a. about 0.75 percentcarbon; b. about 25 percent chromium; c. about 11 percent nickel; d.about 3 percent boron; e. about 2.75 percent silicon; f. a maximum of 1percent iron; g. about 10 percent tungsten; and h. a balance of cobalt;and the subsequent layer of hard facing prior to application comprises:a. from about 0.9 percent to 1.4 percent carbon; b. a maximum of 0.1percent manganese; c. from about 0.4 to about 2.0 percent silicon; d.from about 26 to 32 percent chromium; e. up to 3 percent nickel; f. upto 1 percent molybdenum; g. from about 3 to about 6 percent tungsten; h.up to 3 percent iron; and i. a balance of cobalt.
 12. The processclaimed in claim 11 wherein the subsequent zone of hard facing prior toapplication comprises: a. about 1.3 percent carbon; b. about 1.2 percentsilicon; c. about 28.5 percent chromium; d. about 0.75 percent nickel;e. less than 0.05 percent molybdenum; f. about 4.45 percent tungsten;and g. less than 1 percent iron.